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Two widespread misconceptions regarding Tc are dealt with. First, it is shown that although primordial Tc has decayed completely, Tc is still present in nature due to natural processes, in addition to substantial man-made quantities. Thus, Tc cannot be considered as a purely artificial element. Second, it is shown that 99mTc from 99Mo/99mTc generators is certainly not carrier-free (CF) and that, “no-carrier-added” (NCA) is a more appropriate designation. As a quantitative measure of the amount of long-lived 99gTc carrier present in 99mTc preparations from generators, the Isotope Dilution Factor (IDF) is used and calculated for some practical situations.

Lanthanide emissions to the environment increase as a result of the growing industrial applications of these elements. However, robust data to evaluate the environmental fate of lanthanides are scarce. This article describes the accumulation and elimination of lanthanum (La) by common duckweed (Lemna minor L.). Speciation modeling was performed to assure that solubility products were not exceeded. It also showed that La was predominantly associated with ethylenediaminetetraacetic acid (EDTA). Lanthanum concentrations in plants and medium and the amounts sorbed to glass vessels were quantified by using the radioisotope 140La. The amount of La adsorbed on the glass reached values of 25% of the total La present. A model was formulated to describe La uptake in exponentially growing duckweed in the presence of an adsorptive surface. Growth-induced dilution appeared more efficient in lowering plant La concentrations than actual elimination. An elimination study revealed two compartments, of which the smallest eliminated 50 times faster than the bigger compartment, which eliminated mainly by growth dilution. The average bioconcentration factor was 2,000 L/kg fresh weight and 30,000 L/kg dry weight, comparable with those of other higher plants. At the applied concentration of 10 nM, no effects were observed on duckweed growth. However, the high bioconcentration factor warrants monitoring of lanthanide emissions.

A novel analytical approach was applied to a conventional free-ion selective extraction technique in order to determine the lability of five copper complexes, viz. Cu–CDTA, Cu–EDTA, Cu–NTA, Cu–DTPA, and Cu–humic acid. The main purpose of this approach was to visualise dissociation kinetics of the copper complexes and to exclude reactions other than complex dissociation from the visualisation process. Therefore, three major modifications were applied to a conventional free-ion extraction with Chelex-100: (a) free-ligand concentrations were minimised, (b) the mobile phase as well as column material were provided with a surplus of free copper ions, and (c) the sample under study was equilibrated with a negligible mass of a high-specific activity 64 Cu radiotracer. The actual determination of copper complex lability was carried out in two different ways, either directly, by following dissociation reactions, or indirectly, by following association reactions. The two procedures were given different operationally defined detection windows, to maximise dissociation rate constant determinations. In a region where both detection windows overlapped, similar dissociation rate constants were found for the same copper species. Two species could be distinguished kinetically for Cu–CDTA, Cu–EDTA, as well as Cu–NTA. The dissociation rate constants of these two species differed about two orders of magnitude. The two main chemical forms of Cu–DTPA (viz. a 2:1 and 1:1 complex), predicted by speciation calculations, were found as well and equilibrium concentrations of both species were in accordance with theoretical values. Four species of the Cu–humic acid complex could be identified, with dissociation rate constants in a range of three orders of magnitude.

The technique of Positron Emission Particle Tracking (PEPT) is applied to analyse non-intrusively solids flow in a laboratory scale Interconnected Fluidized Beds system. It is shown that, with a high performance tracking system, it is possible to extract from the data not only the Eulerian ensemble average velocity field, but also to reconstruct density profiles and to calculate mass flows in a solids circulation system. The most interesting flow characteristics inside the Interconnected Fluidized Bed system are highlighted. Although the data analysis is largely Eulerian, a first approach to a Lagrangian analysis has been performed through the computation of velocity autocorrelation functions. Characteristic frequencies of the solids movement could not be identified, but the velocity autocorrelations did provide insight in the dynamics of the solids movement. On a applique la technique de tracage de particules par emission de positrons (PEPT) afin d'analyser l'ecoulement de solides de maniere non intrusive dans un systeme a lits fluidises interrelies a l'echelle du laboratoire. On montre que, avec un systeme de tracage de haute performance, il est possible d'extraire a partir des donnees non seulement le champ de vitesse moyen de l'ensemble eulerien, mais egalement de reconstruire les profils de masse volumique et de calculer les ecoulements massiques dans un systeme de circulation de solides. Les caracteristiques d'ecoulement les plus interessantes dans le systeme a lits fluidises interrelies sont soulignees. Bien que l'analyse soit largement eulerienne, une premiere approche vers une analyse lagrangienne a ete realisee par le calcul des fonctions d'autocorrelation des vitesses. Les frequences caracteristiques du mouvement des solides n'ont pu etre determinees, mais les autocorrelations des vitesses nous eclairent sur la dynamique du mouvement des solides.

This study concerns the bioaccumulation of the long-lived nuclear waste product 99Tc in duckweed (Lemna minor L.). 99Tc was present as the oxyanion TcO4-, being the main chemical form of technetium in aerobic water systems. In contrast with terrestrial plants, bioaccumulation in duckweed proved to be independent of the nitrate concentration in the medium. However, uptake is controlled by electrostatic effects in the cell wall, which affects the bioaccumulation of 99Tc in duckweed in natural environments. These waters are characterized by a range of salinity and hardness, and this study suggests that this may result in up to a threefold difference in 99Tc accumulation. Because of screening of negative charges in the cell wall, the highest accumulation may be expected in hard, brackish water. This behavior can be described by a general model, which includes electrostatic effects and binding of cations at the cell wall. The model also explains why cationic radionuclides are preferably taken up in soft, fresh water while anionic species are concomitantly taken up in hard, chlorine-rich waters.

The uptake of the nuclear waste product technetium-99 was studied in common duckweed (Lemna minor). In addition to measurements, a model involving two compartments in duckweed with different chemical forms of technetium was derived. The model was tested by chemical speciation, i.e. differentiating between reduced Tc-compounds and Tc(VII)O(4)(-). The TcO(4)(-) concentrations measured were in good agreement with those predicted by the model. Two processes determine technetium uptake: (1) transport of Tc(VII)O(4)(-) across the cell membrane, and (2) reduction of Tc(VII). The TcO(4)(-) concentration in duckweed reaches a steady state within 2 h while reduced Tc-compounds are stored, as a result of absence of release or re-oxidation processes. Bioaccumulation kinetic properties were derived by varying 99Tc concentration, temperature, nutrient concentrations, and light intensity. The reduction of technetium in duckweed was highly correlated with light intensity and temperature. At 25 degrees C the maximum reduction rate was observed at light intensities above 200 µmol m(-2) s(-1) while half of the maximum transformation rate was reached at 41 µmol m(-2) s(-1). Transport of TcO(4)(-) over the cell membrane requires about 9.4 kJ mol(-1), indicating an active transport mechanism. However, this mechanism behaved as first-order kinetics instead of Michaelis-Menten kinetics between 1x10(-14) and 2.5x10(-5) mol l(-1) TcO(4)(-). Tc uptake could not be inhibited by 10(-3) mol l(-1) nitrate, phosphate, sulphate or chloride.

Results are presented for the separation of radiolabelled arsenic compounds obtained by the irradiation of organoarsenic compounds in a nuclear reactor. Previously developed chromatographic techniques with element-specific detection were used and further improved to measure the 76 As activities and As concentrations of the arsenic-containing decomposition products formed. Since the recoil energy available during irradiation is high enough to break molecular bonds, a range of radiolabelled arsenic compounds were produced, depending on the conditions (type of compound, matrix and irradiation time). The most extensively investigated compound, viz. arsenobetaine, yielded, when irradiated as solid material for 60 min, 11 radiolabelled arsenic compounds, of which eight could be identified. Theoretically, an overall specific activity of 3.7 GBq g−1 was expected, but experimentally specific activities were found from 0.5 GBq g−1 (for arsenobetaine) to more than 3800 GBq g−1 (for arsenate).

Exchangeable erythrocytic zinc is measured by 65Zn uptake in and release from erythrocytes under standardized and near, physiological conditions: 7.6 microM zinc and 580 microM albumin in the medium. The intracellular exchangeable erythrocytic zinc pool in healthy volunteers amounts to 5 mumol zinc/L packed cells. The half-time of the exchange is 7 h, its activation energy 84 kJ/mol. The effects of the variation in temperature and the concentrations of albumin, as well as the effects of some zinc carriers, cell transport inhibitors, and stress hormones on the 65Zn uptake are measured.

The current paradigm reads that calcifications characterize the advanced and complex lesions in the atherosclerotic process. To explore the possibility that coronary artery wall calcifications already commence at an early stage of atherosclerosis, a combination of proton beam techniques with a (sub-) micrometer resolution, i.e., micro-proton induced X-ray emission, backward and forward scattering spectroscopy, was applied on human coronary arteries with lesions preceding overt atheromas. The detection limits of phosphorus and calcium in each separate pixel, 0.88*0.88 microm2 in size, were approximately 150 and 80 microg/g dry weight, respectively. Calcium distributions of entire coronary artery cross section were obtained, and calcifications were demonstrated at a preatheroma stage of the atherosclerotic process. The size of the microcalcifications varied between 1 and 10 microm. The composition of the microcalcifications was deduced from the calcium-to-phosphorus ratio. In order to quantify this ratio, the thickness of the specific X-ray absorber used for PIXE had to be accurately determined. Also, thick target PIXE calculations were performed and the method was validated. The calcium-to-phosphorus ratios of the microcalcifications were assessed with good accuracy and varied from 1.62 to 2.79, which corresponds with amorphous calcium phosphate.

Aquatic plants may play an important role in the environmental fate of the long-lived radioactive waste product 99Tc. Aquatic plants show a strong accumulation and retention of Tc, even after they have died. This study focuses on possible bio-organic Tc compounds formed in the water dwelling plant duckweed to possibly explain the accumulation and retention. Moreover, a change in chemical speciation often implies a different fate and behaviour in the biosphere. A mild separation technique was used to distinguish between reduced Tc species and TcO(4)(-). Accumulation experiments suggested that reduction of Tc(VII)O(4)(-) and subsequent complexation are responsible for the accumulation of Tc in duckweed. A steady state concentration of TcO(4)(-) in duckweed was reached within 24 h, but the total concentration of Tc increased continuously. Only a small part (/=5%) of Tc was present as TcO(4)(-). Elimination experiments showed that TcO(4)(-) is the only mobile species. Other Tc species are responsible for the retention of Tc in duckweed. It is known that these species are not bio-available and only slowly re-oxidise to pertechnetate, resulting in a longer residence time in ecosystems.

Lanthanide emissions to the environment increase as a result of the growing industrial applications of these elements. However, robust data to evaluate the environmental fate of lanthanides are scarce. This article describes the accumulation and elimination of lanthanum (La) by common duckweed (Lemna minor L.). Speciation modeling was performed to assure that solubility products were not exceeded. It also showed that La was predominantly associated with ethylenediaminetetraacetic acid (EDTA). Lanthanum concentrations in plants and medium and the amounts sorbed to glass vessels were quantified by using the radioisotope 140La. The amount of La adsorbed on the glass reached values of 25% of the total La present. A model was formulated to describe La uptake in exponentially growing duckweed in the presence of an adsorptive surface. Growth-induced dilution appeared more efficient in lowering plant La concentrations than actual elimination. An elimination study revealed two compartments, of which the smallest eliminated 50 times faster than the bigger compartment, which eliminated mainly by growth dilution. The average bioconcentration factor was 2,000 L/kg fresh weight and 30,000 L/kg dry weight, comparable with those of other higher plants. At the applied concentration of 10 nM, no effects were observed on duckweed growth. However, the high bioconcentration factor warrants monitoring of lanthanide emissions.

Industrial emissions of lanthanides to aquatic ecosystems increase, but knowledge of the environmental fate of these metals is limited. Here we focus attention upon the distribution of lanthanides in freshwater ecosystems, describing lanthanide partitioning between sediment, water and biota. Since lanthanides are often used as oxidation-state analogues for actinides, their distribution can reflect long-term behaviour of the radioactive transuranics. Concentrations of all 14 naturally occurring lanthanides were measured by ICP-MS in Sago pondweed (Potamogeton pectinatus), common duckweed (Lemna minor), seven different mollusc species (tissue and shell), two sediment fractions (2 mm and63 microm), surface water and sediment pore water from five locations in The Netherlands. In all samples, the typical 'saw-tooth' lanthanide pattern was observed, which implies that lanthanides are transported as a coherent group through aquatic ecosystems. Typical deviations from this pattern were found for Ce and Eu and could be explained by their redox chemistry. The variation in concentrations in abiotic fractions was limited, i.e. within one order of magnitude. However, variations of up to three orders of magnitude were observed in biotic samples, suggesting different affinities among organisms for lanthanides as a group, with significant differences only among molluscs and pondweed samples in relation to sampling location. For P. pectinatus it was shown that pore water was the most important lanthanide source, and for snails, food (plants) seems to be the dominant lanthanide source. Lanthanides were not equally distributed between mollusc shell and tissue and the ratio of lanthanide concentrations in shell and tissue were dependent on the sampling location. Shells contained much lower concentrations and were relatively enriched in Eu, and to a lesser extent in Ce. Bioconcentration factors for lanthanides in plants and snails relative to surface water were typically between 10000 and 100000 l x kg(-1) dry matter, while sediment-water partition coefficients were between 100000 and 3000000 l x kg(-1) dry matter. There was a low extent of biomagnification in the plant-to-snail system, with a maximum biomagnification factor of 5.5. Many distribution coefficients displayed a slight decrease with atomic number. This can be attributed to the general increase in ligand stability constants with atomic number, keeping the heavier lanthanides preferentially in solution.

A new and simple method is described to plate silicon structures with metallic silver for ultralarge-scale integration in dimensions down to 100 nm at an aspect ratio of 4.25. The silver deposition is initiated by an exchange reaction of silicon with silver ions, and the subsequent layer growth of the activated wafers occurs by electroless plating from supersaturated aqueous silver salt solutions at pH ∼ 11. No extra reducing agents are needed since silver ions are reduced at the catalytic silver surface by hydroxyl ions. The spontaneous ion-metal transition only proceeds at pH ∼ 11 and is likely mediated by the formation of subnanometer-sized [Ag 4 (OH) 2 ] 2+ clusters. The silver plating proceeds more easily in smaller structures and yields void-free, crystallized deposits.

A novel chromatographic technique is described which has prospects for studying the lability of a metal complex in an aqueous system. It is based on interactions of metal species with an ion-exchange column under steady-state conditions. For this purpose, the column is equilibrated with the sample itself by using it as the mobile phase. With the aid of a high specific activity radiotracer, the characteristics of the metal species interaction with the ion-exchange column can be visualized in a radiochromatogram. Under particular experimental conditions, information regarding the dissociation kinetics of the metal complex can be extracted from this radiochromatogram. Erroneous results due to undesirable interactions of metal species with the chromatographic system are prevented, since the system remains in constant chemical equilibrium with the sample to be analyzed. The potential of this technique was investigated with copper complexes, using high specific activity 64Cu for labeling. Preliminary results obtained with four complexes (Cu-EDTA, Cu-NTA, Cu-citrate, and Cu-glycine) are discussed. For three complexes, dissociation rate constants could be determined: (6.2 +/- 0.3) x 10(-3) s(-1) for Cu-EDTA, (1.0 +/- 0.04) x 10(-2) s(-1) for Cu-NTA, and (3.1 +/- 0.2) x 10(-2) s(-1) for Cu-citrate. No dissociation rate constant could be determined for Cu-glycine owing to incompatible experimental conditions.

Environmental Context. Aquatic life requires access to sufficient nutrients and trace metals in the surrounding waters. Measuring the speciation (in solution or precipitated, free ionic or complexed) of trace metals is a traditional procedure to assess the potential of waters for life. Iron, an important nutrient, is relatively insoluble, and metal–ligand complexes are required to keep the iron in solution and bioavailable. Sunlight often degrades these metal–ligand complexes, and the subsequently released iron can outcompete other (trace) metals for their ligands. A ‘domino’ effect on weaker metal–ligand complexes will occur which complicates the actual dynamic speciation and its measurements. Abstract. The effect of photodegradation of iron(iii)-EDTA on the chemical speciation of both iron and cobalt has been tested both in a simple medium and in a more complex algal growth medium. In both media, the photodegradation of iron(iii)-EDTA caused iron(iii) to be released as a free ionic species. Released iron(iii) could be modelled as engaged in precipitation and in competition with cobalt, initially also bound to EDTA. Cobalt appeared as free ionic species after a certain lag. The length of this lag phase was proportional to the amount of EDTA added to the media, which indicated that the surplus of EDTA was first targetted by iron(iii)-EDTA photodegradation, after which iron(iii) out-competed cobalt for the EDTA in the metal–EDTA pool. All data were fitted, using a model on speciation kinetics for cobalt-EDTA and iron(iii)-EDTA, taking into account photodegradation rates of iron(iii)-EDTA and precipitation of free iron(iii). The modelled rate of iron(iii)-EDTA photodegradation was compared to direct HPLC measurements of the disappearance of iron(iii)-EDTA due to photodegradation, the latter, however, with a different iron(iii)-EDTA concentration regime. The results suggest that photodegradation is a complex process which is greatly influenced by experimental conditions (e.g. light intensity/spectrum, iron(iii), and EDTA concentrations). Iron(iii)-desferrioxamine B (DFO-B) was suggested as a possible alternative for EDTA in experimental media: photostability was shown for prolonged experimental periods.

A new and simple method is described to plate silicon structures with metallic silver for ultralarge-scale integration in dimensions down to 100 nm at an aspect ratio of 4.25. The silver deposition is initiated by an exchange reaction of silicon with silver ions, and the subsequent layer growth of the activated wafers occurs by electroless plating from supersaturated aqueous silver salt solutions at pH ∼ 11. No extra reducing agents are needed since silver ions are reduced at the catalytic silver surface by hydroxyl ions. The spontaneous ion-metal transition only proceeds at pH ∼ 11 and is likely mediated by the formation of subnanometer-sized [Ag 4 (OH) 2 ] 2+ clusters. The silver plating proceeds more easily in smaller structures and yields void-free, crystallized deposits.